Mechanical Properties of Elastic Thread Force Systems in Canine Exposures

Objectives: To identify differences in the modulus of elasticity, maximum tensile stress at breakage and tensile stress at maximum load between an elastic thread force system and gold chain with elastic thread force system for impacted canines.

Methods: A circular portion of elastic thread was cut, tied and measured to the nearest hundredth of a millimeter and recorded. Five links of a gold chain were cut and elastic thread was tied to the fifth link opposite the bondable eyelet. The length of the elastic thread as well as gold chain and elastic were measured to the hundredth of a millimeter and recorded. An Instron Universal Testing Machine, with a ramp speed (strain-rate or cross-head speed) of 100 mm/min, was used for all material testing; n=6 for both groups.
Results: The addition of the gold chain, as compared to the elastic thread alone, increased the modulus from 8.8 MPa (SD 3.7) to 17.0 MPa (SD 5.0), (p< 0.04) and significantly decreased the maximum tensile stress at breakage from 92.1N (SD 5.0) to 84.1N (SD 1.6), (p<0.004) and the tensile stress at maximum load from 107.8 N (SD 6.7) to 93.8N (SD 4.8), (p<0.002). The stress-strain curve for both groups demonstrated initial linear behavior followed by non-linear behavior due to the inherent nature of the elastic thread.
Conclusions: The addition of gold chain significantly decreased the toughness and resiliency while introducing a rigid element by replacing one-half the length of the elastic, thereby apparently increasing the modulus of the assembly. A significantly higher modulus implies similar amounts of tooth movement may occur at significantly greater force/strain levels when a gold chain is incorporated. Therefore, elastic thread alone delivers a more constant and continuous force to the tooth.